Orthogonal frequency division multiplexing (OFDM) is a method of encoding digital data on multiple carrier frequencies. In one example, 600 subcarriers are used, which are modulated with data points. There are a large number of closely spaced orthogonal sub-carrier signals used to carry data on several streams. In OFDM, rectangular pulses are transmitted in time. Because the pulses are rectangular in time, inter-symbol interference (ISI) may be eliminated using a guard period between symbols. In OFDM, the subcarriers are orthogonal, eliminating inter-carrier interference (ICI).
OFDM-offset quadrature amplitude modulation (OQAM) is another multicarrier transmission method which uses different shaped pulses with multiple sub-carriers. Pulse shapes with good side lobe properties in the frequency domain and/or time domain may be chosen. Pulse shapes used may include root raised cosine (RRC) pulse, isotropic orthogonal transform algorithm (IOTA) pulse, sinc function pulses, Bellanger pulses, etc. OFDM-OQAM has good power spectral density (PSD) side lobe decay properties. The length of the pulse shape may be at least four symbol lengths to facilitate low ISI, ICI, and good frequency localization. This may lead to ISI and ICI, because the OFDM-OQAM symbols span more than one symbol time period. When one antenna is used in OFDM-OQAM, the pulses are real-orthogonal. Because the pulses are real-orthogonal, the ISI may be removed.